From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 86B6D6B026B for ; Mon, 2 Jul 2018 09:40:45 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id z11-v6so5690133edq.17 for ; Mon, 02 Jul 2018 06:40:45 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id b20-v6si610764edt.361.2018.07.02.06.40.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 Jul 2018 06:40:44 -0700 (PDT) Date: Mon, 2 Jul 2018 15:40:43 +0200 From: Michal Hocko Subject: Re: [RFC v3 PATCH 2/5] mm: introduce VM_DEAD flag Message-ID: <20180702134043.GW19043@dhcp22.suse.cz> References: <1530311985-31251-1-git-send-email-yang.shi@linux.alibaba.com> <1530311985-31251-3-git-send-email-yang.shi@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1530311985-31251-3-git-send-email-yang.shi@linux.alibaba.com> Sender: owner-linux-mm@kvack.org List-ID: To: Yang Shi Cc: willy@infradead.org, ldufour@linux.vnet.ibm.com, akpm@linux-foundation.org, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, tglx@linutronix.de, hpa@zytor.com, linux-mm@kvack.org, x86@kernel.org, linux-kernel@vger.kernel.org On Sat 30-06-18 06:39:42, Yang Shi wrote: > VM_DEAD flag is used to mark a vma is being unmapped, access to this > area will trigger SIGSEGV. > > This flag will be used by the optimization for unmapping large address > space (>= 1GB) in the later patch. It is 64 bit only at the moment, > since: > * we used up vm_flags bit for 32 bit > * 32 bit machine typically will not have such large mapping > > All architectures, which support 64 bit, need check this flag in their > page fault handler. This is implemented in later patches. Please add a new flag with its users. There is simply no way to tell the semantic from the above description and the patch as well. > Suggested-by: Michal Hocko > Signed-off-by: Yang Shi > --- > include/linux/mm.h | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index a0fbb9f..28a3906 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -242,6 +242,12 @@ extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *, > #endif > #endif /* CONFIG_ARCH_HAS_PKEYS */ > > +#ifdef CONFIG_64BIT > +#define VM_DEAD BIT(37) /* bit only usable on 64 bit kernel */ > +#else > +#define VM_DEAD 0 > +#endif > + > #if defined(CONFIG_X86) > # define VM_PAT VM_ARCH_1 /* PAT reserves whole VMA at once (x86) */ > #elif defined(CONFIG_PPC) > -- > 1.8.3.1 -- Michal Hocko SUSE Labs